Datasheet

TPS54262-Q1
www.ti.com SLVS996C –SEPTEMBER 2009–REVISED JUNE 2010
Step 11. Calculate Resistors to Control Slew Rate (R7)
The value of slew rate resistor (R7) can be approximately determined from Figure 24 and Figure 25 at different
typical input voltages. The minimum recommended value is 10 kΩ. To achieve rise time, t
r
= 20 ns and fall time,
t
f
= 35 ns, the slew rate resistor is approximately of value 30 kΩ.
Step 12. Resistors to Select Undervoltage, Overvoltage and Reset Threshold Values (R1, R2, R3)
The sum of these three resistors should be approximately equal to 100 kΩ. In this example,
VReg_OV = 106% of V
Reg
= 5.3 V
VReg_RST = 92% of V
Reg
= 4.6 V
VReg_UV = 95% of V
Reg
= 4.75 V
Using Equation 12, R3 = 15 kΩ.
Using Equation 11, R2 = 2.29 kΩ.
Using Equation 10, R1 = 82.6 kΩ
Step 13. Diode D1 and D2 Selection
Diode D1 is used to protect the IC from the reverse input polarity connection. The diode should be rated at
maximum load current. Only Schottky diode should be connected at the PH pin. The recommended part numbers
are PDS360 and SBR8U60P5.
Step 14. Noise Filter on RST_TH and OV_TH Terminals (C9 and C10)
Typical capacitor values for RST_TH and OV_TH pins are between 10 pF to 100 pF for total resistance on
RST_TH/ OV_TH divider of less than 200 kΩ.
Step 15. Power Budget and Temperature Estimation
Using Equation 25, conduction losses for typical input voltage are calculated to be, P
CON
= 0.289 W.
Assuming slew resistance R7 = 30 kΩ, from Figure 24 and Figure 25, rise time, t
r
= 20 ns and fall time, t
f
= 35
ns. Using Equation 26, switching losses for typical input voltage are calculated to be, P
SW
= 0.693 W.
Using Equation 27, gate drive losses are calculated to be, P
Gate
= 3 mW.
Using Equation 28, power supply losses are calculated to be, P
IC
= 1.8 mW.
Using Equation 29, the total power dissipated by the device is calculated to be, P
Total
= 987 mW.
Using Equation 31, and knowing the thermal resistance of package = 35°C/W, the rise in junction temperature
due to power dissipation is calculated to be, ∆T = 34.5°C.
Using Equation 32, for a given maximum junction temperature 150°C, the maximum ambient temperature at
which the device can be operated is calculated to be, T
A-Max
= 115°C (approximately).
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